So, there is no straight forward way that I can think of. But, what I would do is set a channel variable and log it somewhere:

exten => s,n,Set(VM_UNIQUEID=${UNIQUEID}) exten => s,n,VoiceMail(${EXTEN}@default)

If you are using AGI or ARI, you can log it somewhere useful so you can correlate later.

If you are using a more vanilla configuration I’d say use the voicemail metadata .txt file that will be in the same folder as the recording to get info to find the CDR. It has things like callerid, origmailbox, origdate (or maybe it’s origtime), and duration. origmailbox should match the CDR destination and the orig time should also match. Haven’t done this specifically. But, I’m hoping I’m pointing you in the right direction.

I work with Freeswitch almost exclusively these days. But, my first experience with VoIP was Asterisk and a huge Perl AGI file keeping everyone talking to each other. Those were good time!